1. Field of the Invention
This invention relates to a transport belt used to transport a transport object to a preset position in a high accuracy, and a process for its manufacture. More particularly, this invention relates to a transport belt used to transport recording mediums such as paper and OHP film used in image-forming apparatus such as copying machines, laser beam printers, facsimile machines, ink-jet printers and composite machines of any of these.
2. Related Background Art
As a conventional means for transporting such recording mediums used in electrophotographic apparatus such as copying machines, known is a resin belt formed of a single layer or multiple layer having been controlled to an appropriate resistance value the both sides of which belt is electrostatically charged to impart electric charges to its surface so that the recording mediums can be transported while being attracted thereto by the aid of the electric charges.
In contrast thereto, as shown in FIG. 17, a resin belt 101 on the outer surface or inner surface of which pairs of comb-tooth-shaped electrodes 102 and 103 are continuously formed in the state they engage with one another leaving constant gaps 104 is also known as disclosed in Japanese Patent Publication No. 57-58872. According to this construction, positive and negative voltages are applied to the electrodes 102 and 103, respectively, where a recording medium 105 is transported while being electrostatically locally more strongly attracted to the belt. This electrostatic-attraction transport belt provided with the comb-tooth-shaped electrodes enables stronger attraction of the recording medium to transport it more stably than the one which transport the recording medium only by the aid of the charging of the resin belt as in the above.
Ink-jet recording apparatus of a full-line type making use of a line type recording head having a large number of ejection orifices arranged in the width direction of recording paper to be fed as the recording medium enable achievement of much higher recording speed, and it is more effective to use the above electrostatic-attraction transport belt. As an example in which such an electrostatic-attraction transport belt is used in an ink-jet recording apparatus, one disclosed in Japanese Patent Application Laid-Open No. 11-151842 is available.
As methods used conventionally to manufacture transport belts, available are a heat-melting extrusion method as typified by blown-film extrusion (inflation) and a casting method in which a resin or its precursor is brought into a melt which is then coated on the inner surface and outer surface of a tubular mold in a stated quantity, followed by removal of solvent, and thereafter films formed are peeled.
A method is also disclosed in Japanese Patent Application Laid-Open No. 8-187773 by the present inventors, in which a thermoplastic sheetlike film is wound around a cylindrical member in such a way that the film itself substantially overlaps at its both ends, which is then covered on its outside with a tubular mold member having a smaller coefficient of thermal expansion than the cylindrical member, and these are heated to narrow the gap between the cylindrical member and the tubular mold member and fuse the sheetlike film at its both ends while pressing the ends with a force, to manufacture a tubular film.
To manufacture such an electrostatic-attraction transport belt provided with the comb-tooth-shaped electrodes on the outer surface or inner surface of the belt, it is necessary to prepare the resin belt by the heat-melting extrusion, the casting or the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 8-187773, and join the resin belt, which serve as a base sheet, to a sheet on which an electrode pattern has previously been formed, or form an electrode pattern by various printing on the resin belt formed.
Especially, recording mediums have come required to be transported at a higher speed as the recording speed of image-forming apparatus has been made higher. Hence, in the conventional example in which the resin belt formed of a single layer or multiple layer is charged so that the recording medium can be attraction-transported, there has been a problem that the recording medium may come apart upward from the resin belt without completely resisting the air resistance acting on the recording medium during its transport. As the cause thereof, it is considered that physical external force such as vibration of the belt makes the recording medium tend to come apart upward from the resin belt, or that, when used in ink-jet recording apparatus, the dropping of ink on the recording medium may temporarily lower the resistance value of belt surface to lessen the surface electric charges which attract the recording medium.
Accordingly, in order to achieve higher recording speed of such ink-jet recording type image-forming apparatus, it is preferable to use as the transport belt a composite belt like the one described above, provided with the comb-tooth-shaped electrodes which enable the recording medium to be strongly and continuously electrostatically attracted to the surface of the transport belt.
Where such a composite belt provided with the comb-tooth-shaped electrodes is manufactured by the heat-melting extrusion method (such as blown-film extrusion), it is usually necessary to continuously wind up the transport belt having been produced in a tubular form. However, when such a tubular belt is folded when it is wound up and if any fold is made, the fold may inevitably affect the images to be recorded on the recording medium. On the other hand, if, in order to prevent it, the transport belt thus produced is cut into endless belts as it is kept tubular, a long forming line must be provided to require a large space, resulting in a high manufacture cost.
Where the composite belt provided with the comb-tooth-shaped electrodes is manufactured by the casting method, there is a problem that much cost is required because the management of concentration of solutions and the control of drying atmosphere must accurately be made in order to obtain films with uniform thickness and also the solvent vapor occurring in the drying step must be disposed of.
The composite belt provided with the comb-tooth-shaped electrodes can also be manufactured by preparing the resin belt by the heat-melting extrusion, the casting or the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 8-187773, and thereafter forming thereon the electrode pattern by various printing. In such a case, however, as a matter of course, a higher manufacture cost should result for the part corresponding to the formation of the electrode pattern than in the case of the resin belt prepared by the heat-melting extrusion, the casting or the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 8-187773,